Re: message-Id has localhost

[Ken Hornstein]

>> 2) The recommendation for Message-IDs is to use a domain name for the
>>    right-hand side
>
>Recommendation or rule?  I don't recall.

Officially, from RFC 5322 §3.6.4:

      Note: As with addr-spec, a liberal syntax is given for the right-
      hand side of the "@" in a msg-id.  However, later in this section,
      the use of a domain for the right-hand side of the "@" is
      RECOMMENDED.  Again, the syntax of domain constructs is specified
      by and used in other protocols (e.g., [RFC1034], [RFC1035],
      [RFC1123], [RFC5321]).  It is therefore incumbent upon
      implementations to conform to the syntax of addresses for the
      context in which they are used.
[...]
   The message identifier (msg-id) itself MUST be a globally unique
   identifier for a message.  The generator of the message identifier
   MUST guarantee that the msg-id is unique.  There are several
   algorithms that can be used to accomplish this.  Since the msg-id has
   a similar syntax to addr-spec (identical except that quoted strings,
   comments, and folding white space are not allowed), a good method is
   to put the domain name (or a domain literal IP address) of the host
   on which the message identifier was created on the right-hand side of
   the "@" (since domain names and IP addresses are normally unique),
   and put a combination of the current absolute date and time along
   with some other currently unique (perhaps sequential) identifier
   available on the system (for example, a process id number) on the
   left-hand side.  Though other algorithms will work, it is RECOMMENDED
   that the right-hand side contain some domain identifier (either of
   the host itself or otherwise) such that the generator of the message
   identifier can guarantee the uniqueness of the left-hand side within
   the scope of that domain.

>> 4) Some people, for reasons I would classify as "vague", prefer to
>>    generate their Message-IDs locally so their saved copy of the
>>    message has the Message-ID in it.
>
>The reason you state seems precise rather than vague.

I mean, that's not a reason in my thinking?  Like, WHY do people
want that?  That's where things get vague when this came up before.

>> 7) There's not too much prior art here to crib from because of (3).
>
>The first-hop MTAs would be a source of prior art.  Most probably let
>the domain part be given as configuration.

Well, I was talking about prior art from MUAs.  For MTAs that represent
an email domain, it's relatively straightforward because they assume
that they're the only one generating Message-IDs for that email domain.

FWIW, I took a quick look at the MTAs Postfix and Sendmail; Postfix does
not seem to have any Message-ID-specific configuration knobs, it hardcodes
adding a Message-ID based on it's idea of the local hostname.  Sendmail,
yes, it looks like you could change it if you really want to; it also
defaults to something based on the local hostname.  I am personally
skeptical that people actually configure this.

And, well, we TRY to use the local hostname to generate the Message-ID
for the people who actually want that (because being unique is a MUST in
RFC 5322).  But as we've seen there's not a fullproof way of doing that.

>I think the existing -messageid option which takes either ‘local’ or
>‘random’ should also accept ‘@...’ to allow the user to specify it.
>This stops using heuristics if the user prefers.

My personal feeling is that the people who (a) care about generating a
local Message-ID, and (b) actually care WHAT appears right of the '@'
either need to configure their system appropriately or write code to
change nmh behavior.

--Ken